Test file for issue #17

Cause of the bug is not clear yet... Suspecting a missing default value return
somewhere.

More tests need to be done.
Issue #17: disable test...

This is not really a bug.

As the OP mentions, the problem here is that a Boolean is returned instead of a
boolean. The real "fix", if any, would be to have a BooleanVar.

See also issue #19.
BaseParser: change rule generation in sequence()

This is done in order to match the behaviour of parboiled1.